Vapor and liquid flow

Use the Naphtali-Sandholm SC method to compute stage temperatures and interstage vapor and liquid flow rates and compositions for the rehoiled-stripper specifications shown in Fig. 13-53. The specified hottoms rate is equivalent to removing most of the nCs and nCe and some of the nC in the hottoms. 

Convergence was achieved in 3 iterations. Converged values of temperatures, total flows, and component flow rates are tabulated in Table 13-14. Computed reboiler duty is 1,295,000 W (4,421,000 Btu/h). Computed temperature, total vapor flow, and component flow profiles, shown in Fig. 13-54, are not of the shapes that might be expected. Vapor and liquid flow rates for nC4 change dramatically from stage to stage. 

Calculate internal vapor and liquid flows. (Lr/D)fnin = assumed Solve for (Lr/Vr)min 1... 

The Brown and Martin [9] curve of Figure 8-49 is also used in about the same manner, and produces essentially the same results, but is based on internal vapor and liquid flows. 

The idealized picture of the flow in a heated micro-channel is shown in Fig. 8.1a. Such flow possesses a number of specific properties due to its unique structure, which forms because of liquid evaporation and the interaction of pure vapor and liquid flows separated by the interface surface. The latter has an infinitely thin surface with a jump in pressure and velocity, while the temperature is equal. One can... 

An equilibrium-flash calculation (using the same equations as in case A above) is made at each point in time to find the vapor and liquid flow rates and properties immediately after the pressure letdown valve (the variables with the primes F , F l, y], x j,.. . shown in Fig. 3.8). These two streams are then fed into the vapor and liquid phases. The equations describing the two phases will be similar to Eqs. (3.40) to (3.42) and (3.44) to (3.46) with the addition of (1) a multi-component vapor-liquid equilibrium equation to calculate Pi and (2) NC — 1 component continuity equations for each phase. Controller equations relating 1 to Fi and P to F complete the model. 

TOTCP = heat capacity of combined vapor and liquid flows, including latent... 

Considering that the rings, the grid support, and the I-beam are all in close physical contact, what is the open area at their mutual interface (Answer 80 percent X 75 percent X 90 percent = 54 percent.) This means that there will be a restriction to vapor and liquid flow at the grid support, which will promote flooding at the bottom of the bed. Naturally, this would cause the entire packed bed to flood. 

The volumetric liquid holdup, 4>L, depends on the gas/vapor and liquid flows and is calculated via empirical correlations (e.g., Ref. 65). For the determination of axial temperature profiles, differential energy balances are formulated, including the product of the liquid molar holdup and the specific enthalpy as energy capacity. The energy balances written for continuous systems are as follows ... 

The rate-based models suggested up to now do not take liquid back-mixing into consideration. The only exception is the nonequilibrium-cell model for multicomponent reactive distillation in tray columns presented in Ref. 169. In this work a single distillation tray is treated by a series of cells along the vapor and liquid flow paths, whereas each cell is described by the two-film model (see Section 2.3). Using different numbers of cells in both flow paths allows one to describe various flow patterns. However, a consistent experimental determination of necessary model parameters (e.g., cell film thickness) appears difficult, whereas the complex iterative character of the calculation procedure in the dynamic case limits the applicability of the nonequilibrium cell model. 

The next step is to calculate the pressure loss to the control valve entrance. The designer has located the flow control valve as close as practical to the stabilizer feed entrance. This is a good design location for the control valve. Why The pressure drop across the control valve results in a two-phase flow, vapor and liquid flowing into the stabilizer feed tray. Thus, the downstream flow is a two-phase flow, and this problem will be finished later, in the section on two-phase flow. 

The column diameter is sized to suit the maximum anticipated rates of vapor and liquid flow through the column. Usually, the diameter is determined primarily by the vapor flow rate, and a rough estimate can be obtained from ... 

Columns operated at vapor and liquid flow rates greater than those for which they were designed become flooded. Unexpected foaming can also cause flooding. In a flooded column, liquid cannot properly descend against the upflowing vapor. Poor separation performance results, the overhead condensation circuit fills with process liquid, the reboiler is starved of process liquid, and the column quickly becomes inoperable. 

Conceptually, product quality is determined by the heat balance of the column. The heat removal determines the internal reflux flow rate, whereas the heat addition determines the internal vapor rate. These internal vapor and liquid flow rates determine the degree of separation between two key components. 

Solving the equations simultaneously, D = 71, B = 129. step 2 Set vapor and liquid flow in the column. 

Vapor and liquid flow rates are set in a manner similar to the binary calculation (Sec, 2.2.4), that is,... 

The initial total flow rate and temperature profiles can make the difference between success and failure of a rigorous method. Usually for distillation columns, the condenser and reboiler temperatures are estimated and a calculation that assumes constant molal overflow Sec. 2.2.2) is used to initialize tbe internal vapor and liquid flow... 

The independent variables for this global Newton method will be the bulk component vapor and liquid flow rates compositions at the interface for each component less one a mass transfer rate for each component and the temperatures of the bulk vapor, bulk liquid, and the interface ... 

To ensure uniform resistance to vapor and liquid flow throughout the bed Concentrated pockets of aerodynamic resistance can lower the effective tower cross-section area, thus reducing capacity. 

Element geometry. Due to the corrugations, vapor and liquid flow through a single element spreads in a series of parallel planes. In order to spread the vapor and liquid uniformly in all radial planes, each element is rotated at a certain angle with respect to the element below. The angle of rotation is the angle (in a "horizontal" plane) between the parallel layers in one element and between the parallel layers in an element above (or below). 

In a distillation column, vapor and liquid flow in countercurrent directions to each other. Liquid is vaporized at the bottom, and vapor is condensed from the top product and withdrawn from the column. A number of trays are placed in the column, or the column is packed with open material, so that the vapor phase contacts the liquid phase, and components are transferred from one phase to the other. As you proceed up the column the temperature decreases, and the net effect is an increase in the more volatile component(s) in the vapor and a decrease in the less volatile components in the liquid. Vapor is withdrawn from the top of the column and liquid from the bottom. Feed to the column usually enters part way up the column. 

Calculate the heat-transfer coefficient using both mechanisms and select the higher value calculated as the effective heat-transfer coefficient hL. The annular-flow assumption results in heat-transfer coefficients that vary along the tube length. The condenser should be broken into increments, with the average vapor and liquid flow rates for each increment used to calculate heat-transfer coefficients. The total is the integrated value of all the increments. 

Vapor Shear Controlling For vertical in-tube condensation with vapor and liquid flowing concurrently downward, if gravity controls, Figs. 5-7 and 5-8 may be used, if vapor shear controls, the Carpenter-Colburn correlation (General Discussion on Heat Transfer, London, 1951, ASME, New York, p. 20) is applicable ... 

Since the total vapor and liquid flow rates are, by definition, the sum of the component flow rates of the respective phases, the summation equations and total mass balance equation are satisfied automatically. Thus, the number of equations and variables per stage has been reduced by 2 to 2c + 1. 

Example 3 Simple Distillation Column Compute stage temperatures, interstage vapor and liquid flow rates and compositions, and reboiler and condenser duties for the butane-pentane splitter studied in Example 1. The specifications for this problem are summarized below and in Fig. 13-37. 

Flow profiles are shown in Fig. 13-42c. Note the step change in the liquid flow rate around the feed stage. Had the feed been partially vaporized, we would have observed changes in both vapor and liquid flows around the feed stage, and a saturated vapor feed would significantly change only the vapor flow... 

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